The present invention relates to a heat sensitive actuator to be used as a driving source for an engine coolant thermostat, for example.
It is known that such an actuator includes a casing, a thermal expansion fluid such as wax contained in the casing, and a piston rod inserted in the casing and adapted to be moved outside the casing by thermal expansion of the fluid.
In the above known actuator, a sealing member formed of an elastic material such as rubber is normally provided in an opening end portion of the casing. The sealing member is compressed in an axial direction of the piston rod upon assembling of the actuator. By such a compression force, the sealing member is elastically deformed to be expanded in a radial direction of the piston rod and be pressed against an outer circumference of the piston rod, thereby sealing the fluid.
It is originally necessary to prevent leakage of the fluid at a sealing portion between the sealing member and the piston rod. Further, it is also necessary to reduce a frictional resistance of the piston rod upon movement thereof so that a high sensitivity to heat and a low hysteresis in operation may be ensured.
To meet these requirements in the above-mentioned known actuator, the compression force to be applied to the sealing member must be strictly set so as to properly control the pressing force to be applied to the piston rod. However, as the compression force to be applied to the sealing member is normally given by caulking upon assembling of the actuator, the compression force is largely dispersed, and the proper control of the pressing force is difficult. Accordingly, a product quality is rendered ununiform to cause the generation of leakage of the fluid or excess frictional resistance of the piston rod.